Liquid dispenser

ABSTRACT

The present invention relates to an apparatus for controlled rate dispensing of a liquid contained in a flexible bag, said apparatus including a chamber adapted to contain the flexible bag containing the liquid, an outlet from the chamber adapted to receive an outlet conduit communicating with the interior of the flexible bag, a source of gas arranged to apply pressure to at least part of the exterior walls of the flexible bag, and a pressure regulator arranged to control the pressure applied to said exterior walls, whereby pressure applied to said exterior walls causes liquid to be dispensed from the flexible bad through the outlet conduit at a controlled rate. A method of delivering liquid at a controlled rate using the apparatus of the present invention is also described.

This invention relates to a liquid dispenser and has been devisedparticularly though not solely for low flow rate dispensing of medicalliquids for intravenous drip applications.

There are many situations where it is desirable to be able to provide acontrolled low flow rate delivery of a liquid from a compact, portableand reliable device. In particular, there are many medical situations inwhich it is desirable to supply liquids such as intravenous drip fluidsfor patients in a reliable and easily regulated device which at the sametime is compact and portable so that it is convenient for the patient touse.

In the past, low flow rate dispensing devices, and in particularintravenous drip supply devices, have been provided in a number ofdifferent formats including the conventional gravity feed bag which istypically hung from a support rack located above the patient. Suchdevices are cumbersome for the patient to use, requiring the feeding ofa tube from a fixed and elevated situation to the point of dispensing onthe patient and furthermore they are not readily portable.

Alternative portable devices for the supply of intravenous drip fluidsfor patients have included a round bag with a spring loaded containerwhich is expensive to manufacture, incorporates a screw mechanism whichis difficult to load for some patients, and which does not always ensurea linear delivery of fluid. Other devices include an elastomer deviceincorporating a container with a balloon which is fully disposable andtypically loaded by a hypodermic syringe. These devices are expensive touse due to their “one use” configuration, have limitations on the volumeof fluid contained (typically 50 millilitres) and must be filled by ahealth care professional. There are also syringe drivers, which aretypically powered by electric motors and again are expensive both toprovide and maintain.

There are also many other non-medical applications such as the supply oflubricating fluids to machinery, the dosing of antibacterial fluids intocooling towers or air conditioning systems, and other similarapplications which require a compact and reliable apparatus forcontrolled rate low flow dispensing of liquids.

Accordingly, the present invention provides an apparatus for controlledrate dispensing of a liquid contained in a flexible bag, said apparatusincluding a chamber adapted to contain the flexible bag containing theliquid, an outlet from the chamber adapted to receive an outlet conduitcommunicating with the interior of the flexible bag, a source of gasarranged to apply pressure to at least part of the exterior walls of theflexible bag, and a pressure regulator arranged to control the pressureapplied to said exterior walls, whereby pressure applied to saidexterior walls causes liquid to be dispensed from the flexible bagthrough the outlet conduit at a controlled rate.

In one embodiment of the invention, the chamber is a substantiallygas-tight chamber, the outlet from the chamber is adapted to seal theoutlet conduit to the chamber, and the source of gas is arranged tosupply gas under pressure to the interior of the chamber, therebyapplying pressure to the exterior walls of the flexible bag. In thisembodiment, the pressure regulator is preferably arranged to regulatethe flow of gas from the source of gas to the chamber.

In an alternative embodiment of the invention, the source of gas isconnected to an inflatable bladder such that, in use, the inflatablebladder is in contact with an exterior wall of the flexible bag. Anadvantage of this arrangement is that it obviates the need for asubstantially gas-tight chamber having seals. This type of chamber isrelatively easy to manufacture and eliminates the potential problem ofgas leaking through seals in the chamber.

In this alternative embodiment the inflatable bladder is preferably alsoin contact with an inside wall of the chamber, in use. Preferably, theinflatable bladder comprises an inflatable sock adapted to wrap aroundat least part of the flexible bag. Such an arrangement is advantageous,because it applies a substantially even pressure to the exterior wallsof the flexible bag and allows a substantially constant rate of flow ofliquid from the bag. Preferably, in this alternative embodiment, thepressure regulator is arranged to regulate flow of gas from the sourceof gas to the inflatable bag.

Preferably, the source of gas comprises a pressure vessel ofpre-compressed gas.

Alternatively, the source of gas comprises a reservoir pressurised by apump.

Preferably, the flexible bag is a medical supply bag of the type used tosupply intravenous drip fluids for patients.

Preferably, the flexible bag comprises a so-called Baxter bag.

Preferably, the apparatus is arranged to dispense liquids at acontrolled low flow rate.

The low flow rate may be, for example, less than 100 millilitres perhour (ml/hr), less than 50 ml/hr, less than 25 ml/hr, or less than 10ml/hr.

Preferably, the chamber is provided in a relatively flat cuboidalconfiguration having a depth significantly less than the length or widthof the chamber.

Preferably, the pressure vessel and gas regulator are located alongsidethe chamber in a common housing arranged such that the pressure vesseland gas regulator are contained within the depth of the housing. Thisarrangement allows convenient use and/or transportation of theapparatus.

Preferably, the housing is provided with a support strap adapting thehousing to be worn by a patient.

The present invention further provides a method of delivering liquidfrom a flexible bag at controlled rate, said method including the stepsof providing an apparatus as defined in any one of the preceding claims,setting the pressure regulator to a predetermined pressure, and applyingpressure to at least part of the exterior walls of the flexible bag.

Notwithstanding any other forms that may fall within its scope, twopreferred forms of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional plan view through a first liquid dispensingapparatus according to the invention,

FIG. 2 is a front view of the apparatus shown in FIG. 1,

FIG. 3 is a cross-sectional elevation on the line AA of FIG. 1, and

FIG. 4 is a similar view to FIG. 1 showing a flexible bag containingliquid in place within the chamber of the apparatus.

FIG. 5 is a cross-sectional plan view through a second liquid dispensingapparatus according to the invention.

FIG. 6 is a cross-sectional elevation along the line AA of FIG. 5.

FIG. 7 is a cross-sectional elevation along the line BB of FIG. 5.

FIG. 8 is a cross-sectional elevation similar to FIG. 7, showing theapparatus in an open position.

FIG. 9 is a schematic cross-sectional elevation of the second liquiddispensing apparatus according to the invention.

FIG. 10 is a graph displaying the results of a first liquid dispensingtest performed on the apparatus shown in FIG. 5.

FIG. 11 is a graph displaying the results of a second liquid dispensingtest performed on the apparatus shown in FIG. 5.

In a first preferred form of the invention, a liquid dispensingapparatus particularly designed for dispensing intravenous drip fluidsto patients is constructed as follows, although it will be appreciatedthat the apparatus can be used for other applications and provided inother configurations.

The apparatus comprises a substantially gas tight cuboidal chamber 1typically defined by solid plastics components formed for example ofacrylic or polycarbonate materials. The plastics components define sidewalls 2 and 3 to the chamber, an end wall 4, and a removable cap wall 5.The chamber is completed by face plate portions 6 and 7 and formed intoa gas tight configuration by the use of O-ring seals 8.

The chamber 1 is sized to receive a full medical supply bag such as aBaxter bag shown in FIG. 4 at 9.

The Baxter bag is typically provided with a filling conduit 10 which isaccommodated within a recess 11 in the cap 5 and an outlet conduit 12which is located within an outlet 13 from the chamber 1 which in turn isprovided with a seal 14 arranged to seal the outer periphery of theoutlet conduit 12 to the cap 5, thus maintaining the gas tight nature ofthe chamber 1.

The outlet 12 may be connected to the ultimate dispensing point e.g. toan intravenous drip needle by way of the commonly known flexible tube(not shown).

The apparatus is further provided with a source of gas in the form of apressure vessel 15 which is similar to the type used to providepressurised gas such as CO₂ or air for an inflatable life jacket orother similar uses. There is also provided a pressure regulator 16arranged to regulate the supply of gas from the pressure vessel 15 andfeed that gas into chamber 1 through conduit 17 located within thehousing such that the gas pressure within chamber 1 is maintained at arelatively constant and predetermined level.

The pressure regulator 16 may take any known form, although typicallycomprises the compression spring controlled piston device shown in FIGS.1 and 4 using needle valves to regulate and control the gas supplypressure. It will be appreciated however that many different types ofpressure regulators are well known and could be substituted for theregulator shown at 16.

It is an advantageous feature of the preferred embodiment of theinvention that both the pressure vessel 15 and the gas regulator 16 canbe located alongside the chamber 1 as shown in FIGS. 1 and 4 with thesupply and regulation devices contained within the overall depth of thehousing as can be clearly seen in FIG. 2. This results in a compact andeasy to handle apparatus while still retaining good access to themounting for the pressure vessel 15, enabling the pressure vessel to beeasily changed and replaced as needed.

In use, the pressure regulator 16 is either pre-calibrated, or adjusted,to provide a supply of gas through conduit 17 into chamber 1 calculatedto maintain a predetermined gas pressure within chamber 1 regardless ofthe volume of fluid contained at any point in time in the bag 9. In thismanner, the dispensing force on the liquid within the bag 9 is constantover the full range of the bag, from fill to empty, ensuring a constantflow rate of fluid from the bag through the outlet conduit 12, againstthe back pressure of any regulating device that may be installed in thesupply line connected to the outlet conduit. This enables an extremelyaccurate flow rate of liquid to be achieved over the entire dispensingrange from the bag 9.

It is a further feature of the invention, that the gas pressure withinthe chamber 1 enables all of the liquid within the bag to be dispensed,again providing accurate measurement of total fluids dispensed to apatient, and providing efficient utilisation of all liquid within thebag.

Because the housing formed by the members 2, 3, 4, 5, 6, and 7, and thefurther housing 18 supporting the pressure regulator and pressurevessel, are arranged in a relatively flat cuboidal configuration havinga depth significantly less than the length or width of the chamber, theresulting apparatus is very compact and easy to wear by a patient. Theapparatus can easily be provided with a support strap in the form ofeither a waistband or a shoulder strap (not shown), adapting the housingto be worn by a patient in a position where it is extremely easy andconvenient to lead a supply tube from the outlet conduit 12 to thedispensing point on the body of the patient.

Although the apparatus has been described with the source of gas asbeing a pressure vessel of pre-compressed gas, it will be appreciatedthat other alternatives could be used such as a hand pump pressurisedreservoir contained within or connected to the apparatus. Similarly,other configurations of pressure regulator could be used either toregulate the supply between the source of gas and the chamber as shownin the accompanying drawings or as a pressure relief valve in thechamber to control the build up of pressure within the chamber.

In a second preferred form of the invention, and with reference to FIGS.5-9, a housing 19 is formed from plastics components, such as acrylic orpolycarbonate materials. The housing 19 is similar in design to thehousing shown in FIGS. 1-4 However, the housing lacks the O-ring seals 8shown in FIG. 1. The housing 19 includes a recess 20 and a chamber 30.The recess accommodates a source of gas, in the form of a pressurevessel 21, and an associated pressure regulator 22. The pressure vessel21 and pressure regulator are typically of the same or similar design tothose described above in connection with the first preferred form of theinvention. Furthermore, as in the first preferred form, the recess 20allows convenient and compact design of the liquid dispenser.

A conduit 23 connects the pressure regulator 22 to an inflatable bladder24, which takes the form of an elongate gas sock. The inflatable bladder24 is accommodated in the chamber 30 and substantially fills the spacedefined by the chamber 30. The pressure regulator 22 is used to set thepressure inside the inflatable bladder 24 to a constant andpredetermined pressure. The inflatable bladder 24 may be formed from anyinflatable material, such as plastics or rubber. Such materials will bewell known to the skilled person and are typically used in themanufacture of balloons and the like.

Referring now to FIGS. 7 and 9, the gas sock 24 is wrapped around asubstantial part of a bag 25, which will typically be a Baxter bag, asexemplified in FIG. 4. In the embodiment shown in FIGS. 7 and 9, thebladder 24 is in contact with both the inside wall of the chamber 30 andthe exterior walls of the bag 25. Hence, when the bladder 24 is inflatedby gas delivered from the conduit 23, it squeezes the bag 25 and forcesliquid 26 out of the bag through a conduit 27. The conduit 27 passesthrough an outlet 28 in the housing 19 and communicates with theinterior of the bag 25. An advantage of this second preferred form ofthe invention is that the outlet 28 need not seal the conduit 27 to thechamber 19. All the gas used to force liquid from the bag 25 iscontained in the bladder 24, obviating the need for gas-seals in thechamber.

As shown in FIG. 8, a side wall 31 may be hingedly opened from thehousing 19. A fastener 32 is used to fasten the side wall 31 in a closedconfiguration when required. This hinged arrangement allows convenientaccess to the bag 25 for replacement of liquid or replacement of thebag. Moreover, the side wall 31 need not be sealed against the housingwith gas seals, allowing facile design of the housing.

Other embodiments of the present invention will also be readily apparentto the person skilled in the art. For example, the chamber may includeone or two internal diaphragms having a flexible membrane, themembrane(s) being in contact with the flexible bag. When the diaphragmis pressurized by a source of gas, it expands, thereby causing themembrane to exert a pressure on the exterior walls of the flexible bag.This and other embodiments are contemplated within the scope of thepresent invention.

EXAMPLES

An apparatus according to the second form described above was used todispense liquid from a Baxter bag in two separate runs. In each run, thebag size was 50 mls and the pressure regulator was set to deliver 41.5kPa of pressure from the gas cylinder. The amount of liquid dispensedfrom the bag was measured at one minute intervals.

The results of these two separate runs are displayed graphically in FIG.10 (“Open Sock Test 1”) and FIG. 11 (“Open Sock Test 2”).

The apparatus according to the present invention provides substantiallylinear flow of a liquid from a Baxter bag. In the case of this Example,the rate of flow is about 50 ml/hour. However, it will appreciated thatother flow rates are, of course, possible, depending on the pressure ofgas set by the pressure regulator.

1. An apparatus for controlled rate dispensing of a liquid contained ina flexible bag, said apparatus including a chamber adapted to containthe flexible bag containing the liquid; an outlet from the chamberadapted to receive an outlet conduit communicating with the interior ofthe flexible bag; a source of gas arranged to apply pressure to at leastpart of the exterior walls of the flexible bag; and a pressure regulatorarranged to control the pressure applied to said exterior walls, wherebypressure applied to said exterior walls causes liquid to be dispensedfrom the flexible bag through the outlet conduit at a controlled rate.2. The apparatus according to claim 1, wherein the chamber is asubstantially gas-tight chamber; the outlet from the chamber is adaptedto seal the outlet conduit to the chamber; and the source of gas isarranged to supply gas under pressure to the interior of the chamber,thereby applying pressure to the exterior walls of the flexible bag. 3.The apparatus according to claim 1, wherein the pressure regulator isarranged to regulate flow of gas from the source of gas to the chamber.4. The apparatus according to claim 1, wherein the source of gas isconnected to an inflatable bladder such that, in use, the inflatablebladder is in contact with at least part of an exterior wall of theflexible bag.
 5. (canceled)
 6. (canceled)
 7. The apparatus according toclaim 4, wherein the inflatable bladder comprises an inflatable sockadapted to wrap around at least part of the flexible bag.
 8. (canceled)9. The apparatus according to claim 1, wherein the source of gascomprises a pressure vessel of pre-compressed gas.
 10. The apparatusaccording to claim 1, wherein the source of gas comprises a reservoirpressurised by a pump.
 11. The apparatus according to claim 1, whereinthe flexible bag is a medical supply bag of the type used to supplyintravenous drip fluids for patients.
 12. (canceled)
 13. (canceled) 14.The apparatus according to claim 1, wherein the chamber is provided in arelatively flat cuboidal configuration have a depth significantly lessthan the length or width of the chamber.
 15. The apparatus according toclaim 14, wherein the pressure vessel and gas regulator are locatedalongside the chamber in a common housing arranged such that thepressure vessel and gas regulator are contained within the depth of thehousing.
 16. (canceled)
 17. (canceled)
 18. (canceled)